/**
 * @file
 *
 * Common 6LowPAN routines for IPv6. Uses ND tables for link-layer addressing.
 * Fragments packets to 6LowPAN units.
 *
 * This implementation aims to conform to IEEE 802.15.4(-2015), RFC 4944 and RFC
 * 6282.
 * @todo: RFC 6775.
 */

/*
 * Copyright (c) 2015 Inico Technologies Ltd.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Ivan Delamer <delamer@inicotech.com>
 *
 *
 * Please coordinate changes and requests with Ivan Delamer
 * <delamer@inicotech.com>
 */

/**
 * @defgroup sixlowpan 6LoWPAN (RFC4944)
 * @ingroup netifs
 * 6LowPAN netif implementation
 */

#include "netif/lowpan6_common.h"

#if LWIP_IPV6

#include "lwip/ip.h"
#include "lwip/pbuf.h"
#include "lwip/ip_addr.h"
#include "lwip/netif.h"
#include "lwip/udp.h"

#include <string.h>

/* Determine compression mode for unicast address. */
s8_t lowpan6_get_address_mode(const ip6_addr_t *ip6addr,
                              const struct lowpan6_link_addr *mac_addr) {
    if (mac_addr->addr_len == 2) {
        if ((ip6addr->addr[2] == (u32_t)PP_HTONL(0x000000ff)) &&
            ((ip6addr->addr[3] & PP_HTONL(0xffff0000)) ==
             PP_NTOHL(0xfe000000))) {
            if ((ip6addr->addr[3] & PP_HTONL(0x0000ffff)) ==
                lwip_ntohl((mac_addr->addr[0] << 8) | mac_addr->addr[1])) {
                return 3;
            }
        }
    } else if (mac_addr->addr_len == 8) {
        if ((ip6addr->addr[2] ==
             lwip_ntohl(((mac_addr->addr[0] ^ 2) << 24) |
                        (mac_addr->addr[1] << 16) | mac_addr->addr[2] << 8 |
                        mac_addr->addr[3])) &&
            (ip6addr->addr[3] ==
             lwip_ntohl((mac_addr->addr[4] << 24) | (mac_addr->addr[5] << 16) |
                        mac_addr->addr[6] << 8 | mac_addr->addr[7]))) {
            return 3;
        }
    }

    if ((ip6addr->addr[2] == PP_HTONL(0x000000ffUL)) &&
        ((ip6addr->addr[3] & PP_HTONL(0xffff0000)) == PP_NTOHL(0xfe000000UL))) {
        return 2;
    }

    return 1;
}

#if LWIP_6LOWPAN_IPHC

/* Determine compression mode for multicast address. */
static s8_t lowpan6_get_address_mode_mc(const ip6_addr_t *ip6addr) {
    if ((ip6addr->addr[0] == PP_HTONL(0xff020000)) && (ip6addr->addr[1] == 0) &&
        (ip6addr->addr[2] == 0) &&
        ((ip6addr->addr[3] & PP_HTONL(0xffffff00)) == 0)) {
        return 3;
    } else if (((ip6addr->addr[0] & PP_HTONL(0xff00ffff)) ==
                PP_HTONL(0xff000000)) &&
               (ip6addr->addr[1] == 0)) {
        if ((ip6addr->addr[2] == 0) &&
            ((ip6addr->addr[3] & PP_HTONL(0xff000000)) == 0)) {
            return 2;
        } else if ((ip6addr->addr[2] & PP_HTONL(0xffffff00)) == 0) {
            return 1;
        }
    }

    return 0;
}

#if LWIP_6LOWPAN_NUM_CONTEXTS > 0
static s8_t lowpan6_context_lookup(const ip6_addr_t *lowpan6_contexts,
                                   const ip6_addr_t *ip6addr) {
    s8_t i;

    for (i = 0; i < LWIP_6LOWPAN_NUM_CONTEXTS; i++) {
        if (ip6_addr_net_eq(&lowpan6_contexts[i], ip6addr)) {
            return i;
        }
    }
    return -1;
}
#endif /* LWIP_6LOWPAN_NUM_CONTEXTS > 0 */

/*
 * Compress IPv6 and/or UDP headers.
 * */
err_t lowpan6_compress_headers(struct netif *netif, u8_t *inbuf,
                               size_t inbuf_size, u8_t *outbuf,
                               size_t outbuf_size, u8_t *lowpan6_header_len_out,
                               u8_t *hidden_header_len_out,
                               ip6_addr_t *lowpan6_contexts,
                               const struct lowpan6_link_addr *src,
                               const struct lowpan6_link_addr *dst) {
    u8_t *buffer, *inptr;
    u8_t lowpan6_header_len;
    u8_t hidden_header_len = 0;
    s8_t i;
    struct ip6_hdr *ip6hdr;
    ip_addr_t ip6src, ip6dst;

    LWIP_ASSERT("netif != NULL", netif != NULL);
    LWIP_ASSERT("inbuf != NULL", inbuf != NULL);
    LWIP_ASSERT("outbuf != NULL", outbuf != NULL);
    LWIP_ASSERT("lowpan6_header_len_out != NULL",
                lowpan6_header_len_out != NULL);
    LWIP_ASSERT("hidden_header_len_out != NULL", hidden_header_len_out != NULL);

    /* Perform 6LowPAN IPv6 header compression according to RFC 6282 */
    buffer = outbuf;
    inptr = inbuf;

    if (inbuf_size < IP6_HLEN) {
        /* input buffer too short */
        return ERR_VAL;
    }
    if (outbuf_size < IP6_HLEN) {
        /* output buffer too short for worst case */
        return ERR_MEM;
    }

    /* Point to ip6 header and align copies of src/dest addresses. */
    ip6hdr = (struct ip6_hdr *)inptr;
    ip_addr_copy_from_ip6_packed(ip6dst, ip6hdr->dest);
    ip6_addr_assign_zone(ip_2_ip6(&ip6dst), IP6_UNKNOWN, netif);
    ip_addr_copy_from_ip6_packed(ip6src, ip6hdr->src);
    ip6_addr_assign_zone(ip_2_ip6(&ip6src), IP6_UNKNOWN, netif);

    /* Basic length of 6LowPAN header, set dispatch and clear fields. */
    lowpan6_header_len = 2;
    buffer[0] = 0x60;
    buffer[1] = 0;

    /* Determine whether there will be a Context Identifier Extension byte or
     * not. If so, set it already. */
#if LWIP_6LOWPAN_NUM_CONTEXTS > 0
    buffer[2] = 0;

    i = lowpan6_context_lookup(lowpan6_contexts, ip_2_ip6(&ip6src));
    if (i >= 0) {
        /* Stateful source address compression. */
        buffer[1] |= 0x40;
        buffer[2] |= (i & 0x0f) << 4;
    }

    i = lowpan6_context_lookup(lowpan6_contexts, ip_2_ip6(&ip6dst));
    if (i >= 0) {
        /* Stateful destination address compression. */
        buffer[1] |= 0x04;
        buffer[2] |= i & 0x0f;
    }

    if (buffer[2] != 0x00) {
        /* Context identifier extension byte is appended. */
        buffer[1] |= 0x80;
        lowpan6_header_len++;
    }
#else  /* LWIP_6LOWPAN_NUM_CONTEXTS > 0 */
    LWIP_UNUSED_ARG(lowpan6_contexts);
#endif /* LWIP_6LOWPAN_NUM_CONTEXTS > 0 */

    /* Determine TF field: Traffic Class, Flow Label */
    if (IP6H_FL(ip6hdr) == 0) {
        /* Flow label is elided. */
        buffer[0] |= 0x10;
        if (IP6H_TC(ip6hdr) == 0) {
            /* Traffic class (ECN+DSCP) elided too. */
            buffer[0] |= 0x08;
        } else {
            /* Traffic class (ECN+DSCP) appended. */
            buffer[lowpan6_header_len++] = IP6H_TC(ip6hdr);
        }
    } else {
        if (((IP6H_TC(ip6hdr) & 0x3f) == 0)) {
            /* DSCP portion of Traffic Class is elided, ECN and FL are appended
             * (3 bytes) */
            buffer[0] |= 0x08;

            buffer[lowpan6_header_len] = IP6H_TC(ip6hdr) & 0xc0;
            buffer[lowpan6_header_len++] |= (IP6H_FL(ip6hdr) >> 16) & 0x0f;
            buffer[lowpan6_header_len++] = (IP6H_FL(ip6hdr) >> 8) & 0xff;
            buffer[lowpan6_header_len++] = IP6H_FL(ip6hdr) & 0xff;
        } else {
            /* Traffic class and flow label are appended (4 bytes) */
            buffer[lowpan6_header_len++] = IP6H_TC(ip6hdr);
            buffer[lowpan6_header_len++] = (IP6H_FL(ip6hdr) >> 16) & 0x0f;
            buffer[lowpan6_header_len++] = (IP6H_FL(ip6hdr) >> 8) & 0xff;
            buffer[lowpan6_header_len++] = IP6H_FL(ip6hdr) & 0xff;
        }
    }

    /* Compress NH?
     * Only if UDP for now. @todo support other NH compression. */
    if (IP6H_NEXTH(ip6hdr) == IP6_NEXTH_UDP) {
        buffer[0] |= 0x04;
    } else {
        /* append nexth. */
        buffer[lowpan6_header_len++] = IP6H_NEXTH(ip6hdr);
    }

    /* Compress hop limit? */
    if (IP6H_HOPLIM(ip6hdr) == 255) {
        buffer[0] |= 0x03;
    } else if (IP6H_HOPLIM(ip6hdr) == 64) {
        buffer[0] |= 0x02;
    } else if (IP6H_HOPLIM(ip6hdr) == 1) {
        buffer[0] |= 0x01;
    } else {
        /* append hop limit */
        buffer[lowpan6_header_len++] = IP6H_HOPLIM(ip6hdr);
    }

    /* Compress source address */
    if (((buffer[1] & 0x40) != 0) ||
        (ip6_addr_islinklocal(ip_2_ip6(&ip6src)))) {
        /* Context-based or link-local source address compression. */
        i = lowpan6_get_address_mode(ip_2_ip6(&ip6src), src);
        buffer[1] |= (i & 0x03) << 4;
        if (i == 1) {
            MEMCPY(buffer + lowpan6_header_len, inptr + 16, 8);
            lowpan6_header_len += 8;
        } else if (i == 2) {
            MEMCPY(buffer + lowpan6_header_len, inptr + 22, 2);
            lowpan6_header_len += 2;
        }
    } else if (ip6_addr_isany(ip_2_ip6(&ip6src))) {
        /* Special case: mark SAC and leave SAM=0 */
        buffer[1] |= 0x40;
    } else {
        /* Append full address. */
        MEMCPY(buffer + lowpan6_header_len, inptr + 8, 16);
        lowpan6_header_len += 16;
    }

    /* Compress destination address */
    if (ip6_addr_ismulticast(ip_2_ip6(&ip6dst))) {
        /* @todo support stateful multicast address compression */

        buffer[1] |= 0x08;

        i = lowpan6_get_address_mode_mc(ip_2_ip6(&ip6dst));
        buffer[1] |= i & 0x03;
        if (i == 0) {
            MEMCPY(buffer + lowpan6_header_len, inptr + 24, 16);
            lowpan6_header_len += 16;
        } else if (i == 1) {
            buffer[lowpan6_header_len++] = inptr[25];
            MEMCPY(buffer + lowpan6_header_len, inptr + 35, 5);
            lowpan6_header_len += 5;
        } else if (i == 2) {
            buffer[lowpan6_header_len++] = inptr[25];
            MEMCPY(buffer + lowpan6_header_len, inptr + 37, 3);
            lowpan6_header_len += 3;
        } else if (i == 3) {
            buffer[lowpan6_header_len++] = (inptr)[39];
        }
    } else if (((buffer[1] & 0x04) != 0) ||
               (ip6_addr_islinklocal(ip_2_ip6(&ip6dst)))) {
        /* Context-based or link-local destination address compression. */
        i = lowpan6_get_address_mode(ip_2_ip6(&ip6dst), dst);
        buffer[1] |= i & 0x03;
        if (i == 1) {
            MEMCPY(buffer + lowpan6_header_len, inptr + 32, 8);
            lowpan6_header_len += 8;
        } else if (i == 2) {
            MEMCPY(buffer + lowpan6_header_len, inptr + 38, 2);
            lowpan6_header_len += 2;
        }
    } else {
        /* Append full address. */
        MEMCPY(buffer + lowpan6_header_len, inptr + 24, 16);
        lowpan6_header_len += 16;
    }

    /* Move to payload. */
    inptr += IP6_HLEN;
    hidden_header_len += IP6_HLEN;

#if LWIP_UDP
    /* Compress UDP header? */
    if (IP6H_NEXTH(ip6hdr) == IP6_NEXTH_UDP) {
        /* @todo support optional checksum compression */

        if (inbuf_size < IP6_HLEN + UDP_HLEN) {
            /* input buffer too short */
            return ERR_VAL;
        }
        if (outbuf_size < (size_t)(hidden_header_len + 7)) {
            /* output buffer too short for worst case */
            return ERR_MEM;
        }

        buffer[lowpan6_header_len] = 0xf0;

        /* determine port compression mode. */
        if ((inptr[0] == 0xf0) && ((inptr[1] & 0xf0) == 0xb0) &&
            (inptr[2] == 0xf0) && ((inptr[3] & 0xf0) == 0xb0)) {
            /* Compress source and dest ports. */
            buffer[lowpan6_header_len++] |= 0x03;
            buffer[lowpan6_header_len++] =
                ((inptr[1] & 0x0f) << 4) | (inptr[3] & 0x0f);
        } else if (inptr[0] == 0xf0) {
            /* Compress source port. */
            buffer[lowpan6_header_len++] |= 0x02;
            buffer[lowpan6_header_len++] = inptr[1];
            buffer[lowpan6_header_len++] = inptr[2];
            buffer[lowpan6_header_len++] = inptr[3];
        } else if (inptr[2] == 0xf0) {
            /* Compress dest port. */
            buffer[lowpan6_header_len++] |= 0x01;
            buffer[lowpan6_header_len++] = inptr[0];
            buffer[lowpan6_header_len++] = inptr[1];
            buffer[lowpan6_header_len++] = inptr[3];
        } else {
            /* append full ports. */
            lowpan6_header_len++;
            buffer[lowpan6_header_len++] = inptr[0];
            buffer[lowpan6_header_len++] = inptr[1];
            buffer[lowpan6_header_len++] = inptr[2];
            buffer[lowpan6_header_len++] = inptr[3];
        }

        /* elide length and copy checksum */
        buffer[lowpan6_header_len++] = inptr[6];
        buffer[lowpan6_header_len++] = inptr[7];

        hidden_header_len += UDP_HLEN;
    }
#endif /* LWIP_UDP */

    *lowpan6_header_len_out = lowpan6_header_len;
    *hidden_header_len_out = hidden_header_len;

    return ERR_OK;
}

/** Decompress IPv6 and UDP headers compressed according to RFC 6282
 *
 * @param lowpan6_buffer compressed headers, first byte is the dispatch byte
 * @param lowpan6_bufsize size of lowpan6_buffer (may include data after
 * headers)
 * @param decomp_buffer buffer where the decompressed headers are stored
 * @param decomp_bufsize size of decomp_buffer
 * @param hdr_size_comp returns the size of the compressed headers (skip to get
 * to data)
 * @param hdr_size_decomp returns the size of the decompressed headers (IPv6 +
 * UDP)
 * @param datagram_size datagram size from fragments or 0 if unfragmented
 * @param compressed_size compressed datagram size (for unfragmented rx)
 * @param lowpan6_contexts context addresses
 * @param src source address of the outer layer, used for address compression
 * @param dest destination address of the outer layer, used for address
 * compression
 * @return ERR_OK if decompression succeeded, an error otherwise
 */
static err_t lowpan6_decompress_hdr(
    u8_t *lowpan6_buffer, size_t lowpan6_bufsize, u8_t *decomp_buffer,
    size_t decomp_bufsize, u16_t *hdr_size_comp, u16_t *hdr_size_decomp,
    u16_t datagram_size, u16_t compressed_size, ip6_addr_t *lowpan6_contexts,
    struct lowpan6_link_addr *src, struct lowpan6_link_addr *dest) {
    u16_t lowpan6_offset;
    struct ip6_hdr *ip6hdr;
    s8_t i;
    u32_t header_temp;
    u16_t ip6_offset = IP6_HLEN;

    LWIP_ASSERT("lowpan6_buffer != NULL", lowpan6_buffer != NULL);
    LWIP_ASSERT("decomp_buffer != NULL", decomp_buffer != NULL);
    LWIP_ASSERT("src != NULL", src != NULL);
    LWIP_ASSERT("dest != NULL", dest != NULL);
    LWIP_ASSERT("hdr_size_comp != NULL", hdr_size_comp != NULL);
    LWIP_ASSERT("dehdr_size_decompst != NULL", hdr_size_decomp != NULL);

    ip6hdr = (struct ip6_hdr *)decomp_buffer;
    if (decomp_bufsize < IP6_HLEN) {
        return ERR_MEM;
    }

    /* output the full compressed packet, if set in @see lowpan6_opts.h */
#if LWIP_LOWPAN6_IP_COMPRESSED_DEBUG
    {
        u16_t j;
        LWIP_DEBUGF(LWIP_LOWPAN6_IP_COMPRESSED_DEBUG,
                    ("lowpan6_decompress_hdr: IP6 payload (compressed): \n"));
        for (j = 0; j < lowpan6_bufsize; j++) {
            if ((j % 4) == 0) {
                LWIP_DEBUGF(LWIP_LOWPAN6_IP_COMPRESSED_DEBUG, ("\n"));
            }
            LWIP_DEBUGF(LWIP_LOWPAN6_IP_COMPRESSED_DEBUG,
                        ("%2X ", lowpan6_buffer[j]));
        }
        LWIP_DEBUGF(LWIP_LOWPAN6_IP_COMPRESSED_DEBUG,
                    ("\np->len: %d\n", lowpan6_bufsize));
    }
#endif

    /* offset for inline IP headers (RFC 6282 ch3)*/
    lowpan6_offset = 2;
    /* if CID is set (context identifier), the context byte
     * follows immediately after the header, so other IPHC fields are @+3 */
    if (lowpan6_buffer[1] & 0x80) {
        lowpan6_offset++;
    }

    /* Set IPv6 version, traffic class and flow label. (RFC6282, ch 3.1.1.)*/
    if ((lowpan6_buffer[0] & 0x18) == 0x00) {
        header_temp = ((lowpan6_buffer[lowpan6_offset + 1] & 0x0f) << 16) |
                      (lowpan6_buffer[lowpan6_offset + 2] << 8) |
                      lowpan6_buffer[lowpan6_offset + 3];
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                    ("TF: 00, ECN: 0x%" X8_F ", Flowlabel+DSCP: 0x%8" X32_F
                     "\n",
                     lowpan6_buffer[lowpan6_offset], header_temp));
        IP6H_VTCFL_SET(ip6hdr, 6, lowpan6_buffer[lowpan6_offset], header_temp);
        /* increase offset, processed 4 bytes here:
         * TF=00:  ECN + DSCP + 4-bit Pad + Flow Label (4 bytes)*/
        lowpan6_offset += 4;
    } else if ((lowpan6_buffer[0] & 0x18) == 0x08) {
        header_temp = ((lowpan6_buffer[lowpan6_offset] & 0x0f) << 16) |
                      (lowpan6_buffer[lowpan6_offset + 1] << 8) |
                      lowpan6_buffer[lowpan6_offset + 2];
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                    ("TF: 01, ECN: 0x%" X8_F ", Flowlabel: 0x%2" X32_F
                     ", DSCP ignored\n",
                     lowpan6_buffer[lowpan6_offset] & 0xc0, header_temp));
        IP6H_VTCFL_SET(ip6hdr, 6, lowpan6_buffer[lowpan6_offset] & 0xc0,
                       header_temp);
        /* increase offset, processed 3 bytes here:
         * TF=01:  ECN + 2-bit Pad + Flow Label (3 bytes), DSCP is elided.*/
        lowpan6_offset += 3;
    } else if ((lowpan6_buffer[0] & 0x18) == 0x10) {
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                    ("TF: 10, DCSP+ECN: 0x%" X8_F ", Flowlabel ignored\n",
                     lowpan6_buffer[lowpan6_offset]));
        IP6H_VTCFL_SET(ip6hdr, 6, lowpan6_buffer[lowpan6_offset], 0);
        /* increase offset, processed 1 byte here:
         * ECN + DSCP (1 byte), Flow Label is elided.*/
        lowpan6_offset += 1;
    } else if ((lowpan6_buffer[0] & 0x18) == 0x18) {
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                    ("TF: 11, DCSP/ECN & Flowlabel ignored\n"));
        /* don't increase offset, no bytes processed here */
        IP6H_VTCFL_SET(ip6hdr, 6, 0, 0);
    }

    /* Set Next Header (NH) */
    if ((lowpan6_buffer[0] & 0x04) == 0x00) {
        /* 0: full next header byte carried inline (increase offset)*/
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                    ("NH: 0x%2X\n", lowpan6_buffer[lowpan6_offset + 1]));
        IP6H_NEXTH_SET(ip6hdr, lowpan6_buffer[lowpan6_offset++]);
    } else {
        /* 1: NH compression, LOWPAN_NHC (RFC6282, ch 4.1) */
        /* We should fill this later with NHC decoding */
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                    ("NH: skipped, later done with NHC\n"));
        IP6H_NEXTH_SET(ip6hdr, 0);
    }

    /* Set Hop Limit, either carried inline or 3 different hops (1,64,255) */
    if ((lowpan6_buffer[0] & 0x03) == 0x00) {
        LWIP_DEBUGF(
            LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
            ("Hops: full value: %d\n", lowpan6_buffer[lowpan6_offset + 1]));
        IP6H_HOPLIM_SET(ip6hdr, lowpan6_buffer[lowpan6_offset++]);
    } else if ((lowpan6_buffer[0] & 0x03) == 0x01) {
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                    ("Hops: compressed: 1\n"));
        IP6H_HOPLIM_SET(ip6hdr, 1);
    } else if ((lowpan6_buffer[0] & 0x03) == 0x02) {
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                    ("Hops: compressed: 64\n"));
        IP6H_HOPLIM_SET(ip6hdr, 64);
    } else if ((lowpan6_buffer[0] & 0x03) == 0x03) {
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                    ("Hops: compressed: 255\n"));
        IP6H_HOPLIM_SET(ip6hdr, 255);
    }

    /* Source address decoding. */
    if ((lowpan6_buffer[1] & 0x40) == 0x00) {
        /* Source address compression (SAC) = 0 -> stateless compression */
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                    ("SAC == 0, no context byte\n"));
        /* Stateless compression */
        if ((lowpan6_buffer[1] & 0x30) == 0x00) {
            LWIP_DEBUGF(
                LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                ("SAM == 00, no src compression, fetching 128bits inline\n"));
            /* copy full address, increase offset by 16 Bytes */
            MEMCPY(&ip6hdr->src.addr[0], lowpan6_buffer + lowpan6_offset, 16);
            lowpan6_offset += 16;
        } else if ((lowpan6_buffer[1] & 0x30) == 0x10) {
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("SAM == 01, src compression, 64bits inline\n"));
            /* set 64 bits to link local */
            ip6hdr->src.addr[0] = PP_HTONL(0xfe800000UL);
            ip6hdr->src.addr[1] = 0;
            /* copy 8 Bytes, increase offset */
            MEMCPY(&ip6hdr->src.addr[2], lowpan6_buffer + lowpan6_offset, 8);
            lowpan6_offset += 8;
        } else if ((lowpan6_buffer[1] & 0x30) == 0x20) {
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("SAM == 10, src compression, 16bits inline\n"));
            /* set 96 bits to link local */
            ip6hdr->src.addr[0] = PP_HTONL(0xfe800000UL);
            ip6hdr->src.addr[1] = 0;
            ip6hdr->src.addr[2] = PP_HTONL(0x000000ffUL);
            /* extract remaining 16bits from inline bytes, increase offset */
            ip6hdr->src.addr[3] = lwip_htonl(
                0xfe000000UL | (lowpan6_buffer[lowpan6_offset] << 8) |
                lowpan6_buffer[lowpan6_offset + 1]);
            lowpan6_offset += 2;
        } else if ((lowpan6_buffer[1] & 0x30) == 0x30) {
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("SAM == 11, src compression, 0bits inline, using "
                         "other headers\n"));
            /* no information available, using other layers, see RFC6282
             * ch 3.2.2 */
            ip6hdr->src.addr[0] = PP_HTONL(0xfe800000UL);
            ip6hdr->src.addr[1] = 0;
            if (src->addr_len == 2) {
                ip6hdr->src.addr[2] = PP_HTONL(0x000000ffUL);
                ip6hdr->src.addr[3] = lwip_htonl(
                    0xfe000000UL | (src->addr[0] << 8) | src->addr[1]);
            } else if (src->addr_len == 8) {
                ip6hdr->src.addr[2] = lwip_htonl(
                    ((src->addr[0] ^ 2) << 24) | (src->addr[1] << 16) |
                    (src->addr[2] << 8) | src->addr[3]);
                ip6hdr->src.addr[3] =
                    lwip_htonl((src->addr[4] << 24) | (src->addr[5] << 16) |
                               (src->addr[6] << 8) | src->addr[7]);
            } else {
                /* invalid source address length */
                LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                            ("Invalid source address length\n"));
                return ERR_VAL;
            }
        }
    } else {
        /* Source address compression (SAC) = 1 -> stateful/context-based
         * compression */
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                    ("SAC == 1, additional context byte\n"));
        if ((lowpan6_buffer[1] & 0x30) == 0x00) {
            /* SAM=00, address=> :: (ANY) */
            ip6hdr->src.addr[0] = 0;
            ip6hdr->src.addr[1] = 0;
            ip6hdr->src.addr[2] = 0;
            ip6hdr->src.addr[3] = 0;
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("SAM == 00, context compression, ANY (::)\n"));
        } else {
            /* Set prefix from context info */
            if (lowpan6_buffer[1] & 0x80) {
                i = (lowpan6_buffer[2] >> 4) & 0x0f;
            } else {
                i = 0;
            }
            if (i >= LWIP_6LOWPAN_NUM_CONTEXTS) {
                /* Error */
                return ERR_VAL;
            }
#if LWIP_6LOWPAN_NUM_CONTEXTS > 0
            ip6hdr->src.addr[0] = lowpan6_contexts[i].addr[0];
            ip6hdr->src.addr[1] = lowpan6_contexts[i].addr[1];
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("SAM == xx, context compression found @%d: %8" X32_F
                         ", %8" X32_F "\n",
                         (int)i, ip6hdr->src.addr[0], ip6hdr->src.addr[1]));
#else
            LWIP_UNUSED_ARG(lowpan6_contexts);
#endif
        }

        /* determine further address bits */
        if ((lowpan6_buffer[1] & 0x30) == 0x10) {
            /* SAM=01, load additional 64bits */
            MEMCPY(&ip6hdr->src.addr[2], lowpan6_buffer + lowpan6_offset, 8);
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("SAM == 01, context compression, 64bits inline\n"));
            lowpan6_offset += 8;
        } else if ((lowpan6_buffer[1] & 0x30) == 0x20) {
            /* SAM=01, load additional 16bits */
            ip6hdr->src.addr[2] = PP_HTONL(0x000000ffUL);
            ip6hdr->src.addr[3] = lwip_htonl(
                0xfe000000UL | (lowpan6_buffer[lowpan6_offset] << 8) |
                lowpan6_buffer[lowpan6_offset + 1]);
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("SAM == 10, context compression, 16bits inline\n"));
            lowpan6_offset += 2;
        } else if ((lowpan6_buffer[1] & 0x30) == 0x30) {
            /* SAM=11, address is fully elided, load from other layers */
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("SAM == 11, context compression, 0bits inline, using "
                         "other headers\n"));
            if (src->addr_len == 2) {
                ip6hdr->src.addr[2] = PP_HTONL(0x000000ffUL);
                ip6hdr->src.addr[3] = lwip_htonl(
                    0xfe000000UL | (src->addr[0] << 8) | src->addr[1]);
            } else if (src->addr_len == 8) {
                ip6hdr->src.addr[2] = lwip_htonl(
                    ((src->addr[0] ^ 2) << 24) | (src->addr[1] << 16) |
                    (src->addr[2] << 8) | src->addr[3]);
                ip6hdr->src.addr[3] =
                    lwip_htonl((src->addr[4] << 24) | (src->addr[5] << 16) |
                               (src->addr[6] << 8) | src->addr[7]);
            } else {
                /* invalid source address length */
                LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                            ("Invalid source address length\n"));
                return ERR_VAL;
            }
        }
    }

    /* Destination address decoding. */
    if (lowpan6_buffer[1] & 0x08) {
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG, ("M=1: multicast\n"));
        /* Multicast destination */
        if (lowpan6_buffer[1] & 0x04) {
            LWIP_DEBUGF(LWIP_DBG_ON,
                        ("DAC == 1, context multicast: unsupported!!!\n"));
            /* @todo support stateful multicast addressing */
            return ERR_VAL;
        }

        if ((lowpan6_buffer[1] & 0x03) == 0x00) {
            /* DAM = 00, copy full address (128bits) */
            LWIP_DEBUGF(
                LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                ("DAM == 00, no dst compression, fetching 128bits inline\n"));
            MEMCPY(&ip6hdr->dest.addr[0], lowpan6_buffer + lowpan6_offset, 16);
            lowpan6_offset += 16;
        } else if ((lowpan6_buffer[1] & 0x03) == 0x01) {
            /* DAM = 01, copy 4 bytes (32bits) */
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("DAM == 01, dst address form (48bits): "
                         "ffXX::00XX:XXXX:XXXX\n"));
            ip6hdr->dest.addr[0] = lwip_htonl(
                0xff000000UL | (lowpan6_buffer[lowpan6_offset++] << 16));
            ip6hdr->dest.addr[1] = 0;
            ip6hdr->dest.addr[2] = lwip_htonl(lowpan6_buffer[lowpan6_offset++]);
            ip6hdr->dest.addr[3] =
                lwip_htonl((lowpan6_buffer[lowpan6_offset] << 24) |
                           (lowpan6_buffer[lowpan6_offset + 1] << 16) |
                           (lowpan6_buffer[lowpan6_offset + 2] << 8) |
                           lowpan6_buffer[lowpan6_offset + 3]);
            lowpan6_offset += 4;
        } else if ((lowpan6_buffer[1] & 0x03) == 0x02) {
            /* DAM = 10, copy 3 bytes (24bits) */
            LWIP_DEBUGF(
                LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                ("DAM == 10, dst address form (32bits): ffXX::00XX:XXXX\n"));
            ip6hdr->dest.addr[0] = lwip_htonl(
                0xff000000UL | (lowpan6_buffer[lowpan6_offset++] << 16));
            ip6hdr->dest.addr[1] = 0;
            ip6hdr->dest.addr[2] = 0;
            ip6hdr->dest.addr[3] =
                lwip_htonl((lowpan6_buffer[lowpan6_offset] << 16) |
                           (lowpan6_buffer[lowpan6_offset + 1] << 8) |
                           lowpan6_buffer[lowpan6_offset + 2]);
            lowpan6_offset += 3;
        } else if ((lowpan6_buffer[1] & 0x03) == 0x03) {
            /* DAM = 11, copy 1 byte (8bits) */
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("DAM == 11, dst address form (8bits): ff02::00XX\n"));
            ip6hdr->dest.addr[0] = PP_HTONL(0xff020000UL);
            ip6hdr->dest.addr[1] = 0;
            ip6hdr->dest.addr[2] = 0;
            ip6hdr->dest.addr[3] = lwip_htonl(lowpan6_buffer[lowpan6_offset++]);
        }

    } else {
        /* no Multicast (M=0) */
        if (lowpan6_buffer[1] & 0x04) {
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("DAC == 1, stateful compression\n"));
            /* Stateful destination compression */
            /* Set prefix from context info */
            if (lowpan6_buffer[1] & 0x80) {
                i = lowpan6_buffer[2] & 0x0f;
            } else {
                i = 0;
            }
            if (i >= LWIP_6LOWPAN_NUM_CONTEXTS) {
                /* Error */
                return ERR_VAL;
            }
#if LWIP_6LOWPAN_NUM_CONTEXTS > 0
            ip6hdr->dest.addr[0] = lowpan6_contexts[i].addr[0];
            ip6hdr->dest.addr[1] = lowpan6_contexts[i].addr[1];
#endif
        } else {
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("DAC == 0, stateless compression, setting link local "
                         "prefix\n"));
            /* Link local address compression */
            ip6hdr->dest.addr[0] = PP_HTONL(0xfe800000UL);
            ip6hdr->dest.addr[1] = 0;
        }

        /* M=0, DAC=0, determining destination address length via DAM=xx */
        if ((lowpan6_buffer[1] & 0x03) == 0x00) {
            LWIP_DEBUGF(
                LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                ("DAM == 00, no dst compression, fetching 128bits inline\n"));
            /* DAM=00, copy full address */
            MEMCPY(&ip6hdr->dest.addr[0], lowpan6_buffer + lowpan6_offset, 16);
            lowpan6_offset += 16;
        } else if ((lowpan6_buffer[1] & 0x03) == 0x01) {
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("DAM == 01, dst compression, 64bits inline\n"));
            /* DAM=01, copy 64 inline bits, increase offset */
            MEMCPY(&ip6hdr->dest.addr[2], lowpan6_buffer + lowpan6_offset, 8);
            lowpan6_offset += 8;
        } else if ((lowpan6_buffer[1] & 0x03) == 0x02) {
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("DAM == 01, dst compression, 16bits inline\n"));
            /* DAM=10, copy 16 inline bits, increase offset */
            ip6hdr->dest.addr[2] = PP_HTONL(0x000000ffUL);
            ip6hdr->dest.addr[3] = lwip_htonl(
                0xfe000000UL | (lowpan6_buffer[lowpan6_offset] << 8) |
                lowpan6_buffer[lowpan6_offset + 1]);
            lowpan6_offset += 2;
        } else if ((lowpan6_buffer[1] & 0x03) == 0x03) {
            /* DAM=11, no bits available, use other headers (not done here) */
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                        ("DAM == 01, dst compression, 0bits inline, using "
                         "other headers\n"));
            if (dest->addr_len == 2) {
                ip6hdr->dest.addr[2] = PP_HTONL(0x000000ffUL);
                ip6hdr->dest.addr[3] = lwip_htonl(
                    0xfe000000UL | (dest->addr[0] << 8) | dest->addr[1]);
            } else if (dest->addr_len == 8) {
                ip6hdr->dest.addr[2] = lwip_htonl(
                    ((dest->addr[0] ^ 2) << 24) | (dest->addr[1] << 16) |
                    dest->addr[2] << 8 | dest->addr[3]);
                ip6hdr->dest.addr[3] =
                    lwip_htonl((dest->addr[4] << 24) | (dest->addr[5] << 16) |
                               dest->addr[6] << 8 | dest->addr[7]);
            } else {
                /* invalid destination address length */
                LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG,
                            ("Invalid destination address length\n"));
                return ERR_VAL;
            }
        }
    }

    /* Next Header Compression (NHC) decoding? */
    if (lowpan6_buffer[0] & 0x04) {
        LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG, ("NHC decoding\n"));
#if LWIP_UDP
        if ((lowpan6_buffer[lowpan6_offset] & 0xf8) == 0xf0) {
            /* NHC: UDP */
            struct udp_hdr *udphdr;
            LWIP_DEBUGF(LWIP_LOWPAN6_DECOMPRESSION_DEBUG, ("NHC: UDP\n"));

            /* UDP compression */
            IP6H_NEXTH_SET(ip6hdr, IP6_NEXTH_UDP);
            udphdr = (struct udp_hdr *)((u8_t *)decomp_buffer + ip6_offset);
            if (decomp_bufsize < IP6_HLEN + UDP_HLEN) {
                return ERR_MEM;
            }

            /* Checksum decompression */
            if (lowpan6_buffer[lowpan6_offset] & 0x04) {
                /* @todo support checksum decompress */
                LWIP_DEBUGF(LWIP_DBG_ON,
                            ("NHC: UDP chechsum decompression UNSUPPORTED\n"));
                return ERR_VAL;
            }

            /* Decompress ports, according to RFC4944 */
            i = lowpan6_buffer[lowpan6_offset++] & 0x03;
            if (i == 0) {
                udphdr->src = lwip_htons(lowpan6_buffer[lowpan6_offset] << 8 |
                                         lowpan6_buffer[lowpan6_offset + 1]);
                udphdr->dest =
                    lwip_htons(lowpan6_buffer[lowpan6_offset + 2] << 8 |
                               lowpan6_buffer[lowpan6_offset + 3]);
                lowpan6_offset += 4;
            } else if (i == 0x01) {
                udphdr->src = lwip_htons(lowpan6_buffer[lowpan6_offset] << 8 |
                                         lowpan6_buffer[lowpan6_offset + 1]);
                udphdr->dest =
                    lwip_htons(0xf000 | lowpan6_buffer[lowpan6_offset + 2]);
                lowpan6_offset += 3;
            } else if (i == 0x02) {
                udphdr->src =
                    lwip_htons(0xf000 | lowpan6_buffer[lowpan6_offset]);
                udphdr->dest =
                    lwip_htons(lowpan6_buffer[lowpan6_offset + 1] << 8 |
                               lowpan6_buffer[lowpan6_offset + 2]);
                lowpan6_offset += 3;
            } else if (i == 0x03) {
                udphdr->src = lwip_htons(
                    0xf0b0 | ((lowpan6_buffer[lowpan6_offset] >> 4) & 0x0f));
                udphdr->dest = lwip_htons(
                    0xf0b0 | (lowpan6_buffer[lowpan6_offset] & 0x0f));
                lowpan6_offset += 1;
            }

            udphdr->chksum = lwip_htons(lowpan6_buffer[lowpan6_offset] << 8 |
                                        lowpan6_buffer[lowpan6_offset + 1]);
            lowpan6_offset += 2;
            ip6_offset += UDP_HLEN;
            if (datagram_size == 0) {
                datagram_size = compressed_size - lowpan6_offset + ip6_offset;
            }
            udphdr->len = lwip_htons(datagram_size - IP6_HLEN);

        } else
#endif /* LWIP_UDP */
        {
            LWIP_DEBUGF(LWIP_DBG_ON, ("NHC: unsupported protocol!\n"));
            /* @todo support NHC other than UDP */
            return ERR_VAL;
        }
    }
    if (datagram_size == 0) {
        datagram_size = compressed_size - lowpan6_offset + ip6_offset;
    }
    /* Infer IPv6 payload length for header */
    IP6H_PLEN_SET(ip6hdr, datagram_size - IP6_HLEN);

    if (lowpan6_offset > lowpan6_bufsize) {
        /* input buffer overflow */
        return ERR_VAL;
    }
    *hdr_size_comp = lowpan6_offset;
    *hdr_size_decomp = ip6_offset;

    return ERR_OK;
}

struct pbuf *lowpan6_decompress(struct pbuf *p, u16_t datagram_size,
                                ip6_addr_t *lowpan6_contexts,
                                struct lowpan6_link_addr *src,
                                struct lowpan6_link_addr *dest) {
    struct pbuf *q;
    u16_t lowpan6_offset, ip6_offset;
    err_t err;

#if LWIP_UDP
#define UDP_HLEN_ALLOC UDP_HLEN
#else
#define UDP_HLEN_ALLOC 0
#endif

    /* Allocate a buffer for decompression. This buffer will be too big and will
       be trimmed once the final size is known. */
    q = pbuf_alloc(PBUF_IP, p->len + IP6_HLEN + UDP_HLEN_ALLOC, PBUF_POOL);
    if (q == NULL) {
        pbuf_free(p);
        return NULL;
    }
    if (q->len < IP6_HLEN + UDP_HLEN_ALLOC) {
        /* The headers need to fit into the first pbuf */
        pbuf_free(p);
        pbuf_free(q);
        return NULL;
    }

    /* Decompress the IPv6 (and possibly UDP) header(s) into the new pbuf */
    err = lowpan6_decompress_hdr(
        (u8_t *)p->payload, p->len, (u8_t *)q->payload, q->len, &lowpan6_offset,
        &ip6_offset, datagram_size, p->tot_len, lowpan6_contexts, src, dest);
    if (err != ERR_OK) {
        pbuf_free(p);
        pbuf_free(q);
        return NULL;
    }

    /* Now we copy leftover contents from p to q, so we have all L2 and L3
       headers (and L4?) in a single pbuf: */

    /* Hide the compressed headers in p */
    pbuf_remove_header(p, lowpan6_offset);
    /* Temporarily hide the headers in q... */
    pbuf_remove_header(q, ip6_offset);
    /* ... copy the rest of p into q... */
    pbuf_copy(q, p);
    /* ... and reveal the headers again... */
    pbuf_add_header_force(q, ip6_offset);
    /* ... trim the pbuf to its correct size... */
    pbuf_realloc(q, ip6_offset + p->len);
    /* ... and cat possibly remaining (data-only) pbufs */
    if (p->next != NULL) {
        pbuf_cat(q, p->next);
    }
    /* the original (first) pbuf can now be freed */
    p->next = NULL;
    pbuf_free(p);

    /* all done */
    return q;
}

#endif /* LWIP_6LOWPAN_IPHC */
#endif /* LWIP_IPV6 */
